This invention relates generally to conveyor belt type material transport systems and is specifically directed to an endless, laterally bendable belt conveyor system particularly adapted for the continuous face haulage of particulate material up- or downslope and around corners.
Since the introduction of the continuous mining machine in the coal industry in the 1950's, a continuing attempt has been made to replace the intermittent, batch-type haulage system provided by shuttle car face haulage with a conveyor type, continuous face haulage system in order to increase coal transport efficiency and take full advantage of the continuous mining machine. The shuttle car change period inherently reduces continuous mining machine operating time because the miner must stop extracting while waiting for the replacement of a full shuttle car by an empty shuttle car in this sequential loading and removal operation.
Frequently in conveying bulk material in the coal mining environment as well as other industrial applications, it is necessary to transport the material around a corner in a curved displacement path. Generally, a flat conveyor belt is unable to negotiate a transverse curve because its two edges cannot accommodate the difference in length between the inside bend radius and the outside bend radius. In this situation the inside edge collapses because the edge tension cannot be maintained due to the shortened radius. As a result, the transported load on the belt is spilled over the inside while the outer edge of the belt tends to roll up over the conveyor belt pushing the material on the belt toward the inside edge resulting in further spillage of the particulate matter being transported.
There are two basic types of conveyor systems designed for continuous face haulage. One is a string of short, standard, cascading conveyors mounted on mobile vehicular carriers and arranged in a train-like fashion. This approach, with its multiplicity of conveyor drives, has the inherent disadvantage of excessive dust generation and requires the accurate placement of adjacent conveyor sections in order to avoid coal spillage at transfer points. In addition, because this approach relies on a plurality of independently acting conveyor systems, it possesses inherent reliability limitations.
The second basic type of conveyor system for continuous face haulage involves the use of a single, articulated conveyor designed to make lateral turns in an ever-changing path which its mobile frame follows in advancing behind the continuous mining machine. This second approach, which does not suffer from the aforementioned limitations of the cascade-type of conveyor system, has generally followed two lines of development.
One approach includes a belt having outer edges of reduced thickness with guide rollers engaging the edges to hold the edge along the outer transverse bend down and to partially collapse the inner edge as it goes around the inside transverse bend. Typically the belt, which is very expensive, used in such systems is provided with lateral convolutions to permit lateral bending, imbedded wire ropes along its longitudinal center line to accommodate the operating tension of the belt, and lateral steel rods imbedded across the width of the belt to provide load support when the belt travels between intermediate roller supports. Edge rollers mounted on each intermediate roller stand and bearing on the edge of the belt guide the belt along its circuitous path. This type of belt is subject to substantial wear, particularly along the edges which are inherently weak due to reduced thickness. Also, the edges of the belt are subjected to substantial crushing pressure by the guide rollers, creating the tendency to cause premature wearing and fraying of the belt edges. This inevitably leads not only to early belt replacement, but also to the belt jumping out from between the rollers under periodic heavy loading conditions causing spillage and system down time. Examples of conveyor systems utilizing this approach are disclosed in U.S. Pat. Nos. 3,545,598, 3,701,411 and 4,061,223 to McGinnis, and 3,863,752 to Sibley.
The second approach used in non-cascading types of conveyor systems is of a substantially older design than the first approach described above. This approach typically employs a chain-driven, multiple pan conveyor having rigid sides shaped to prevent side spillage of material and an underlying continuous belt that prevents the material from dropping through the clearances between the articulated pans. The fabrication costs of the pans and underlying belt make this approach prohibitively expensive for many applications while conveying capacity for a given belt width and height is limited by pan size. Finally, the interacting metal pans and the chain drive of the system inherently cause excessive wear between adjacent, coupled components and generate excessive noise making this approach less desirable under normal working conditions. Examples of the articulated pan conveyor approach are described in U.S. Pat. Nos. 2,818,962, 2,818,965 and 2,836,283 to Horth, and 3,707,218 to Payne, et al.
Other conveyor belt designs which are modifications of the first approach discussed above can be found in the prior art. One such approach is described in U.S. Pat. No. 4,024,949 to Kleysteuber and the present applicant wherein is described an endless conveyor apparatus having pretensioned elastic beads attached to the load-carrying portion of the conveyor belt to allow the belt to bend transversely so as to accommodate a curve. The pretensioning of the beads traveling in the guide rollers is sufficient so that for the given maximum curve of the conveyor belt there is still sufficient tension in the inside bead to hold up the edge of the load portion. Along the outside transverse bend radius of the conveyor belt, the elasticity of the beads is sufficient to allow the bead to stretch further to a maximum tension thereby accommodating the greater radius without bending over. The preferred conveyor belt is a laterally convoluted, molded belt with wire ropes embedded in its center for absorbing the operating tension to which the belt is subjected. To this convoluted belt are attached pretension elastic edge cords. Since this mechanical attaching must be done in place on the conveyor frame, this approach is somewhat impractical for use in a coal mine environment.
Another approach to the design of an endless conveyor belt system adapted to convey around curves as well as along straight lines is disclosed in U.S. Pat. No. 2,867,315 to Lanier. This system includes a head pulley at one end and a tail pulley at the other end thereof around which the endless conveyor belt passes. The portion of the belt intermediate the head and tail pulleys is supported by a plurality of wheels mounted on the sides of the belt at intervals and positioned to engage a subjacent surface and support the belt without the necessity of providing idler supports. Thus, troughing idlers and return rolls are entirely eliminated in this system. Finally, a closed belt conveyor system making use of an endless zipper belt in which the material transported is completely enclosed is disclosed in "Materials Handling Handbook" by H. A. Bolz as once manufactured by Stephens-Adamson Mfg. Co. The endless zipper belt includes a flat base belt with two flexible side walls hinged to its edges. The outer edges of the side walls are provided with teeth which may interlock to form a complete enclosure for transporting materials which must be isolated from the surroundings. The base is of rubberized fabric plies to provide body and tensile strength, while the side walls are solid rubber with keys molded integrally therein. The belt can be carried around bends on a series of rollers. This approach is not only expensive when compared with conventional conveyor belt designs, but also suffers from reliability problems because of fouling of the zipper by the conveyed, particulate material.
The present invention is intended to overcome the aforementioned problems of the prior art by providing a relatively inexpensive, reliable and efficient endless conveyor belt apparatus which is readily compatible with hostile environments such as found in underground mining operations.